1. Field of the Invention
This invention relates to the field of locking devices for discouraging theft of vehicles such as bicycles, and in particular to a key operated device which either fixes the handlebar assembly relative to the front fork of a bicycle, whereupon the bicycle can be operated, or which decouples the handlebar assembly for free rotation relative to the fork, rendering the bicycle inoperable due to lack of steering control.
2. Prior Art
Bicycle locks usually provide a means for locking together necessarily movable parts of the running or steering gear of the bicycle as a means to prevent theft by disabling the bicycle. Therefore, even though the lock does not attach the bicycle to a fixed location a thief cannot simply drive the bicycle away. For example, a conventional bicycle lock provides a shaft, cable or other structure that can be extended through the spokes of a wheel and locked to the frame to prevent rotation of the wheel. This concept can be extended to a device providing means to lock the front fork at an inoperable orientation relative to the frame of the bicycle, for example fixing the steerable wheel (usually the front wheel) perpendicular to the longitudinal axis of the bicycle. The present invention relates to the reverse form of a lock, wherein the connected mode of the lock allows the bicycle to be ridden by operably attaching parts necessary for steering (the handlebars and the steerable wheel). The disconnected mode of the lock disables operation of the bicycle by releasing these parts, making it impossible to steer the bicycle as necessary to get underway. Control of the steerable wheel is crucial to maintaining balance at low speed.
A bicycle lock of this general description is known as disclosed in International Application PCT/AU89/00462--Orbell, filed Oct. 26, 1989. The connection by which the handlebar stem is fixed to the steerable front fork of the bicycle is provided with a rotationally decoupleable fitting, operated using a key. The handlebars become rotatable relative to the fork for disabling steering of the bicycle, and become rotationally fixed relative to the fork for enabling steering. A shaft member attached to the handlebar clamp is journalled at the front of the bicycle frame and attached to the central vertical tube of the fork using a conventional expandable fitting. The handlebar clamp assembly includes a sleeve member that fits on the top end of the shaft member and the sleeve is rotatable relative to the shaft, but for operation of the lock. The lock has radially movable locking members that in the decoupled mode retract into apertures in the shaft member, and in the coupled mode reside partly in the shaft member and partly in the sleeve. A key operated cylinder rotates a cam urging the locking members radially outwardly through the apertures in the shaft to engage in corresponding receptacles for the rollers in the sleeve. The locking members are cylindrical rollers spaced at 120.degree. around the shaft and sleeve. When the cam is rotated back (i.e., when no radially outward pressure is placed on the rollers), any steering force tends to rotate the sleeve relative to the shaft and causes the rollers to retract into the shaft. This frees the handlebar clamp for rotation relative to the fork and makes it impossible to operate the bicycle. The cylinder lock rotates the cam thirty degrees between the locked position (where the rollers are aligned to the receptacles in the sleeve) and the unlocked position (where the rollers are centered between receptacles). The operator inserts the key only when moving between the locked and unlocked modes, and the key is removable from the lock at either extreme.
Although the Orbell device is useful for the basic function of engaging and disengaging the mechanical connection of the handlebar clamp and the fork, difficulties are encountered in realizing the design in a practical embodiment. Axial connection of the lock parts and the handlebar clamp and fork parts is one area of difficulty. The bolt used to operate the expanding fitting that engages the handlebar clamp shaft or headstem to the fork tube must be accessible for attaching the headstem to the fork through the journal fitting at the front or headstock of the bicycle frame. The handlebar sleeve and cylinder lock therefore must be attached over the end of this bolt after the handlebar clamp shaft is mounted on the fork. According to Orbell, the axial attachment of the parts relies on set screws or "grub screws" which are passed radially through the parts, and also axially to bear against abutments, whereby the respective parts are captured on the headstem. These elements do not provide the precision necessary to ensure that the look elements operate smoothly and dependably, particularly over the useful life of the lock. The mechanism should be smoothly free to rotate when the lock is released and should provide minimal play, preferably no play whatsoever, in the connection between the handlebars and the fork when the lock is engaged. If too much play is provided, which can occur when the axial connection of the parts is loose, the handlebars and the steering fork remain relatively movable somewhat when the locking members are in the coupled position. This condition is quite unsettling to the operator of the bicycle and is unsafe. On the other hand if the mounting is too tight (for example due to binding of the lock as a result of excess axial pressure), the lock becomes ineffective because sufficient frictional engagement between the handlebars and the fork exists in the decoupled position that a thief can steer adequately to get the bicycle under way. Once underway, rotational inertia tends to stabilize the front wheel, and frictional engagement of the coupling may be adequate for operation, although not particularly safe.
In order to operate dependably, a mounting for a lock of this type is needed which is very precise with respect to clearances needed for free relative rotation of the coupled parts, particularly providing precision in the axial pressure applied at the lockable coupling. The mounting must also lock positively when engaged, without play in the coupling. This would enable correct control the frictional engagement of the parts and also allow a very positive engagement in the coupled mode of the lock.
A further problem is encountered with respect to use of the key which operates the lock. According to Orbell, a standard key having a flat finger-manipulated tab is employed and the key can be removed from the lock in either the engaged or disengaged position of the lock. There is no means provided to retain the position of the cylinder lock against displacement by vibration or the like produced by operation of the bicycle. Whereas the angular span of the cylinder lock between the engaged and disengaged positions is only thirty degrees, and no means are provided to retain the lock in position when engaged, an operator of the bicycle suddenly may be confronted with a loss of steering control through the mechanical coupling of the handlebars and the fork, while riding.
The operator of a bicycle according to Orbell presumably could leave the key in the lock when riding, to monitor position of the cylinder lock visually, enabling a quick correction should the connection of the handlebars and the fork become loose due to displacement of the locking cam and cylinder lock. The key, however, is a safety hazard in itself, as its finger tab protrudes from the top of the headstem and may injure the rider in the event of a collision. Furthermore, the key can be lost in transit.
According to the present invention, the sleeve and shaft of a locking connection of the type at issue are securely, precisely and durably attached in a manner providing a minimum of access to the headstem. The axial attachment of the respective parts is provided with conically engaging complementary tapers, including a split tapered or conical bushing supported by a fitted spacer. A split tapered bushing normally would render such a coupling sensitive to axial pressure on the parts, resulting in increased frictional engagement of the coupleable parts of the lock. However, the frictional engagement is precisely controlled notwithstanding normal variations in the parts due to manufacturing tolerances, wear and the like. The device is quite secure when engaged yet very free when disengaged. A particular form of tubular key having a protective cap for the headstem operates the lock. The key has a tubular key stem insertable axially into an annular key opening which is modified such that the key stops positively at either of its extremes of movement. The key is spring biased against the lock pins and has a guide tab which retracts into a capturing receptacle when the lock is in the engaged position. The invention provides an improved headstem locking coupling that is inexpensive, durable, safe and precise.